feat: support model display aliases

[CodePirate7]

Summary

• Allow users to define display aliases for models using model_id:alias syntax in the model input field (e.g., claude-sonnet-4-6:My Sonnet, gpt-5.2:GPT5)
• Aliases are purely cosmetic — the underlying model ID sent to the provider stays the same
• Aliases are stored per-connection via modelAliases: Record<string, string> and shown in model selectors and settings

Motivation

When many models are configured (especially with custom providers), they can be hard to distinguish. Display aliases let users assign memorable short names.

Changes

• packages/shared/src/config/models.ts — Add displayAlias to ModelDefinition; update getModelDisplayName() and getModelShortName() to prefer alias
• packages/shared/src/config/llm-connections.ts — Add modelAliases field to LlmConnection
• packages/shared/src/protocol/dto.ts — Add modelAliases to LlmConnectionSetup DTO
• packages/server-core/src/handlers/rpc/llm-connections.ts — Persist modelAliases in setup handler
• apps/electron/src/renderer/components/apisetup/ApiKeyInput.tsx — Parse model_id:alias format, pass aliases through submit
• apps/electron/src/renderer/hooks/useOnboarding.ts — Thread modelAliases through save config pipeline
• apps/electron/src/renderer/components/app-shell/input/FreeFormInput.tsx — Show aliases in model selector dropdown
• apps/electron/src/renderer/pages/settings/AiSettingsPage.tsx — Show aliases in settings; serialize back to id:alias format when editing

Test plan

• Configure a connection with models using alias syntax: model-id-1:Alias1, model-id-2:Alias2
• Verify aliases appear in the model selector dropdown and settings page
• Verify the actual model ID (not alias) is sent to the provider
• Verify editing an existing connection preserves aliases in the input field
• Verify connections without aliases continue to work unchanged

🤖 Generated with Claude Code